The present invention relates to a clamping apparatus for a molding machine such as an injection molding machine, a die cast machine, and a press molding machine.
A clamping apparatus for clamping a mold whose halves are disposed on a fixed board and a moving board in the following construction is disclosed in Japanese Patent Application Laid-open Document No. SHO 63-317243.
In the clamping apparatus, mold clamping cylinder devices have tie bar insertion holes at four corners of the fixed board disposed on a base. Tie bars each having a thread shaft are disposed at the four corners of the movable board disposed on the base. Half nut connection devices disposed at an outer portion of the fixed board are connected to mold clamping pistons of mold clamping cylinders. As the movable board is moved, the tie bars are inserted into the mold clamping cylinders. Thereafter, the tie bars are connected to the mold clamping pistons by the half nuts.
In the above mentioned clamping apparatus, the connection is made with a thread engagement. Thus, the engagement position is determined in accordance with the thickness of molds to be used and both thread pitches should be matched.
Consequently, unless both the mold halves have been completely closed, the connection cannot be made with the thread engagement. Thus, since a time for which the clamping pressure rises becomes long, the molding cycle tends to have a loss.
Also, since the above-mentioned clamping apparatus outputs a large mold clamping force, mold clamping cylinders with a large diameter are used. Thus, a large amount of hydraulic oil is used, it is of course smaller than that of a direct pressure type clamping apparatus. Conventionally, in one oil chamber, hydraulic oil is supplied, while in other oil chamber, hydraulic oil is drained to the hydraulic circuit. In other words, when the oil chambers on both sides of each mold clamping piston are independently controlled, a pressure rise with a high speed characteristic cannot be accomplished. To accomplish it, a pump with a large delivery amount, a hydraulic pipe with a large diameter allowing a large capacity of hydraulic oil to pass instantaneously, and a valve with a large capacity are required.
Nevertheless, the pump with a large delivery amount has substantially a low response characteristic. To prevent that, it is possible to operate a plurality of pumps with a small capacity in parallel. However, when such a system is used, its construction will become complicated and large and thereby increasing the production cost.
Also, in such an apparatus, the parallelism of the mold mounting surfaces of the fixed board and the movable board should be kept by a particular means unlike another clamping apparatus where a plurality of tie bars disposed on a pair of fixed boards on a machine base are inserted into a movable board, the movable board being movable back and forth relative to the fixed board with a guide of the tie bars. The value of adjustment with respect to the parallelism is very small. In the above-mentioned apparatus according to the prior art, a support which extends in the moving direction is disposed on the left and right sides of the legs of the movable mold plate. On the lower side of the support, a guide mounting plate and a guide block are disposed. The movable mold plate is mounted on the guide rails. The guide mounting plate and the support are slightly rotated so as to relatively offset their positions. In this state, the guide plate and the support are connected at four positions of front, rear, left, and right positions by pins.
In the construction according to the prior art, the stopper bolt is screwed from the inner surface of the support to the guide mounting plate. The stopper bolt whose thread end contacts the guide mounting plate causes the guide mounting plate to relatively deviate from the support so as to adjust the parallelism of the movable mode plate against the fixed mold plate. Thus, the connections of the guide mounting plate and the support are limited only to the above-mentioned four positions which are front, rear, left, and right positions. In addition, the connected portions only withstand the relative deviation. Thus, when the mold halves are frequently clamped, the stopper bolt are loosened and the position of the guide mounting plate deviates, thereby losing the parallelism.
In the conventional clamping apparatus, a movable board is approached to a fixed board and thereby mold clamping pistons of mold clamping cylinders disposed on the fixed board side and tie bars with a thread shaft disposed on the movable board side are closed. Thereafter, a half-nut connected to each mold clamping piston is engaged with the thread shaft of each tie bar to thereby clamp mold halves.
In the clamping apparatus according to the prior art, it is said that the half-nuts and the thread of each tie bar can be matched by moving the half-nuts for a small amount in the longitudinal direction. However, although the half-nuts slidably supported through a bracket are contacted with the end portion of a ram by a spring, the practical construction of the fine adjustment of the engagement positions of the half-nuts and the thread of each tie bar is not shown.
Moreover, in the prior art, when the fixed mold half and the movable mold half are engaged and the end portion of each tie bar passes through and stops at the fixed board, the tie bar is connected to the half-nuts. Thus, the mold closing speed cannot be slowed down with each mold clamping cylinder and thereby the mold halves cannot be properly protected.
In the conventional clamping device for an injection molding machine is equipped with a safety door in a side position thereof for safety of the operator. While the safety door is kept open, the mold closing operation is electrically prohibited. In addition, by considering the worst case, unless the safety door is closed, the mold halves cannot be mechanically closed as a dual safety countermeasure. In a conventional clamping device where a movable board is movably disposed between a pair of fixed boards on a machine base and mold halves are closed by the movable board with a guide of tie bars, a safety rod extends from the movable board to the fixed board which is provided with the mold half. A stopper member for supporting the end portion of the safety rod is vertically movably disposed on the fixed board side. The movable member of the stopper member is disposed at the upper end portion of the safety door. When the safety door is closed, the movable member upwardly pushes the stopper member. Thus, only when the components located at the end portion of the safety rod are removed, the mold halves can be closed. However, in a large clamping device where a pair of a fixed board and a movable board are disposed on the machine base and the movable board is movable back and forth relative to the fixed board with a pair of guide rails disposed on an upper surface of the machine base, no tie bars which are used to support the load of the movable board and to function as guides are used. Thus, when the safety rod which extruding toward the fixed board is mounted on the movable board, the load of the safety rod is applied to the movable board as a localized load. As a result, it is difficult to maintain the parallelism of the movable board relative to the fixed board.
In addition, whenever the mold halves are replaced, the length of the extrusion should be adjusted in accordance with the thickness thereof. Since the safety rod is fixed by nuts, the length of extrusion is adjusted by loosening them. In a small clamping device, such a manual adjustment operation can readily be performed by one person. Nevertheless, when the device becomes large, since the safety rod is heavy, it is difficult to adjust it only by one person.
Also, according to the automatic replacement of mold haves, with respect to labor saving, automatic position adjustment of the safety rod is desired.